Human navigation systems track the motion of a pedestrian as he moves over a space. These navigation systems can be made small enough to be wearable by the pedestrian being tracked. For example, global positioning satellites (“GPS”), electromagnetic emitters/receivers, and inertial units such as accelerometers and gyroscopes have been used in such navigation systems. Inertial tracking devices are dead-reckoning systems which keep track of the current location of a subject by estimating the direction and distance traveled and adding it to a previous location estimate. These may include sophisticated inertial navigation systems, as well as simple pedometer devices which count steps with an accelerometer and may use a gyroscope and/or a compass to determine direction. In this application, the terms “inertial tracking device” and “dead-reckoning device” are used interchangeably to refer to a system which keeps track of a subject's position by accumulating increments of motion. In some cases, such a device may be subject to some drift or error accumulation over time.